The Role of the Mean-State Atmospheric Circulation in Future Projections of Regional Hydroclimate and Cloud Feedbacks

减轻气候风险的努力依赖于模型模拟来确定气候将如何在区域基础上变化，例如随着世界变暖，特定地区的降雨量是增加还是减少。 但在许多地区，气候模型并不能给出一致的答案，例如在美国西南部，一些模型预测夏季降雨量较多，而另一些模型预测较少。缺乏共识可能意味着两种结果的可能性实际上是相等的，现有气候模型集合的预测范围准确地代表了可能结果的范围。 或者，也许应该对范围的某一部分进行折扣，因为该范围内的预测受到特定模型偏差的影响，这些偏差与预测的变化有着明显的动态联系。例如，首席研究员（PI）最近的一项研究将西南部未来降水的预测与美国中部对流层中部脊周围的湿气流联系起来，这些湿气流来自同一模型的现代模拟。产生最强降水增加的模式显示出与当前观测不一致的过度脊化，因此对西南部夏季多雨的预测产生了怀疑。该奖项下的研究继续了PI的努力，以确定影响区域降水变化未来预测的当前大气环流特征，以及对区域云量变化的预测，这可以放大或减少温室气体排放的变暖效应。 这项工作使用模型模拟的统计分析，以确定未来预测和当今环流特征之间的关系，然后使用社区大气模型（CAM），CESM的大气成分模型，社区地球系统模型进行专门的模拟。 这些模拟使用“轻推”来产生模拟若干气候模型的现代模拟，并与海洋表面均匀变暖的模拟相结合，以便评估不同的现代环流的影响，该项目具有社会和科学意义，因为需要更好的信息来指导评估和应对气候风险的努力。 该项目为博士后助理和研究生提供支持和培训，从而促进该研究领域未来的劳动力。此外，该项目通过弗吉尼亚州-北卡罗莱纳少数民族参与联盟的夏季研究计划接待了一名夏季本科生。该奖项反映了NSF的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

Efforts to mitigate climate risk rely on model simulations to determine how climate will change on a regional basis, for instance whether it will rain more or less in a given region as the world warms. But in many regions climate models do not produce consistent answers, for instance in the US Southwest some models project more summer rainfall while others project less. The lack of consensus could mean that either outcome is in fact equally likely, and the range of projections across the ensemble of available climate models is an accurate representation of the range of likely outcomes. Alternatively, perhaps some portion of the range should be discounted because the projections in that range are influenced by specific model biases which have a clear dynamical connection to the projected changes. For instance a recent study by the Principal Investigator (PI) connects projections of future precipitation over the Southwest to the moisture flow around a mid-tropospheric ridge over the central US in present-day simulations from the same models. The models which produce the strongest precipitation increases show excessive ridging which is not consistent with present-day observations, thus casting doubt on their projections of rainier summers in the Southwest.Research under this award continues the PI's effort to identify present-day atmospheric circulation features which affect future projections of regional precipitation change, as well as projections of regional cloud cover change which can amplify or reduce the warming effect of greenhouse gas emissions. The work uses statistical analysis of model simulations to identify relationships between future projections and present-day circulation features, followed by specialized simulations using the Community Atmosphere Model (CAM), the atmospheric component model of CESM, the Community Earth System Model. The simulations use "nudging" to produce present-day simulations which mimic several climate models, paired with simulations in which a uniform warming is applied to the ocean surface so that the effects of the differing present-day circulations can be assessed.The project is of societal as well as scientific interest given the need for better information to guide efforts to assess and respond to climate risk. The project provides support and training to a postdoctoral associate and a graduate student, thereby promoting the future workforce in this research area. In addition, the project hosts a summer undergraduate student through the Virginia-North Carolina Alliance for Minority Participation's summer research program.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.